Experimental setup to measure the wake fields excited by a rough surface

The wake fields generated by electron bunches of high charge density in an undulator vacuum chamber might become sufficiently large to affect the FEL amplification. Recent theoretical and numerical calculations show that, with decreasing the bunch length the dominant contribution to the wake fields comes from the surface roughness of the chamber. The excited radiation field should be detectable outside the vacuum chamber. At the TTF linac an experiment is in preparation to measure the radiation power spectrum excited in beam pipes with an artificially increased roughness on the inner surface. Particularly, the dependence on the radius of the pipe and the shape of the surface will be studied in this experiment. In this paper we describe the experimental setup, detection schemes for the radiation and estimates of systematic background.